-permeable support



'as electrical conductors.

STEN CIL MANS AND MANUFACTURE THEREF Fred E. Kendall, 30550 Landerwood Drive, Chagrin Falls, Ohio Filed May 11, 1955, Ser. No. 507,696

Claims. (Cl. 10i-128.3)

This invention relates as indicated to a novel stencil and method of preparing the same, and more particularly to a method of producing an improved duplicating stencil resist having a much longer life than any heretofore produced. This application is a continuation-in-part of my co-pending application Serial No. 431,685, filed May 24, 1954, for Stencil Manufacture.

For many years duplicating paper or the like has been cut, die-impressed and embossed in the preparation of stencils for use on mimeograph and other types of duplicating machines. More recently, an electrolytic method of marking metals through a die-impressed pressure sensitive resist or engraved plastic resist has been widely accepted by the metal marking industry and is now preferred in contrast to the older methods utilizing steel die stamps, acid and ink stamps, and pantograph or engraving tools. Such electrolytic method has utilized a die-impressed pressure-sensitive paper stencil which has been reinforced with various types of synthetic or natural resins and waxes adapted to be readily displaced by pressure rolling or by impact against electrotype or etched plates. After die-impressing, a liquid marking medium which may be either an ink or an electrolytic fluid, for example, is then applied to the stencil sheet and will pass through the porous fibrous layer where thus exposed and mark an underlying work surface accordingly. There are many modifications of this general marking method, practically all of which are susceptible of improvement in accordance with my present invention.

Stencils of the type above discussed are very convenient of use and give satisfactory results when first employed. 'They are, however, not very long-lived and the results obtained from any one stencil tend to become less and less satisfactory until the stencil must eventually be discarded. Many interested in the stencil problem have attempted to solve it through the technique of applying water soluble colloids containing photosensitive compounds to a supported porous member. After the coating has dried, a photonegative or a photopositive transparency is placed in contact with the coating, and by exposure to a proper light source, some curing of the light exposed coating may be caused to take place. The unexposed area may then be washed out with water and the exposed area treated in a hardening solution.

While the technique last described above has certain obvious virtues, it has also involved certain features which are unfortunate for my purpose. Colloidal proteins which have been light-sensitized with bichromates produce fairly well-defined copy but since they are hydrophilic they never become truly water impermeable but will imbibe water (including electrolytes) and thus serve This obviously renders them unsuitable for electrolytic stencil work.

It is accordingly a principal object of my invention to provide a novel stencil which may be produced by employment of an appropriate photographic negative or 2,969,732 Patented dan. 31, V1961 positive or other mask and which will have sharp definition and an extremely long life.

Another object is to provide a method of manufacturing such stencil which will be relatively simple and expeditious and will not require a high degree of skill on the part of the craftsman.

Still another object is to provide a stencil ofthe type indicated comprising a layer of pervious material and a layer of impervious material wherein such layer of impervious material is relatively thick, Wear-resistant, and impervious to liquids employed therewith, including electrolytes.

Another object is to provide such novel stencil in which the pervious material is strengthened and reinforced with a material compatible with such impervious layer without blocking the pores or interstices therein.

Other objects of the invention will appear as the description proceeds.

To the accomplishment of the foregoing and related ends, said invention then comprises vthe features hereinafter fully described and particularly pointed out in the claims, the following description and the annexed drawing setting forth in detail certain illustrative embodiments of the invention, these being indicative, however, of but a few of the various Ways in which the principle of the invention may be employed.

In said annexed drawing:

Fig. l diagrammatically illustrates the layer of permeable supporting base material coated with a layer of a light sensitive polymeric resin; Y

Fig. 2 diagrammatically illustrates such permeable material coated on both sides with layers of such resin;

Fig. 3 shows the manner in which such material may be exposed to light passing through an appropriate negative to produce exposed and unexposed areas;

Figs. 4 and 5 illustrate the production of finished stencil through solvent development;

Fig. `6 corresponds to Fig. 5 but with both sides of the permeable supporting base coated with the resin;

Fig. 7 is a top plan view of a special vacuum printing frame which I prefer to employ in the production of my new stencil;

Fig. 8 is a longitudinal section taken on the line 8-8 on Fig. 7; and

Figure 9 is a diagrammatic highly magnified view of the permeable or porous base material after it has been strengthened by a preliminary coating of the hereinafter described photosensitive material.

In accordance with my invention, l employ an impervious lm or layer of a synthetic resin on a sheet of pervious material such as Yoshino long fiber paper, such resin or lacquer being photosensitive and rendered insoluble due to photo-chemical action upon exposure to light.

More particularly, I prefer to employ photo-sensitive or photo-reactive resins which are soluble in organic solvents such as the polymeric cinnamic esters which have been photosensitized as taught in Minsk et al. Patent 2,610,120, for example. 'A preferred material comprises a cinnamic acid ester of polyvinyl alcohol as a combined carrier and light sensitive material, and as a sensitizer for the composition a nitro aryl compound having a nucleus containing from 6 to l0 carbon atoms, from l to 3 nitro groups being attached to such nucleus, the mono-nitro compounds being free of amino, hydroxyl, and formyl groups in a position ortho to the nitro group, such nitro aryl compounds being free of an amino and a hydroxyl group in positions ortho to each other, and free of carboxyl and sulpho groups. Reference may be had to said Minsk et al. patent for further details regarding the preparation of such photosensitive coating 3 material and also to Minsk et al. Patents 2,670,285; 2,670,286; and 2,670,287.

Instead of applying an extremely thin lm of the resin to an impervious supporting surface as taught by Minsk et al., l apply a relatively thick lrn of the resin to a permeable medium which may be of no greater thickness than such film itself. This photosensitive resin or lacquer may be applied to one or both sides of such pervious material in any convenient manner. `It readily lends itself to application by Weir coating or by roll coating on automatic equipment. Indeed, it may be applied simply by immersing the supportingmedium (such as Yoshino paper) therein and wiping. off the surplus through xed wiping bars. Conventional spraying techniques familiar in the paint industry may be employed, but this will ordinarily require that the pervious supporting medium be supported in an appropriate frame.

In order to produce my new stencil having. a relatively thick resin coating or coatings without danger of poor development, undercutting, and poor definition, I utilize the novel vacuum printing frame shown in Figs. 7 and 8 of the drawing. Such frame comprises a iiat metal plate l (preferably aluminum) having a narrow groove 2 milled therein parallel to the outer edge of the plate and defining the printing area. Such groove may be about a quarter of an inch deep and a quarter of an inch wide and may be spaced about one inch in from the outer edge of the plate. The printing area 3 of the plate defined by such groove will desirably be milled about 1A@ inch lower than the outer rim of the plate in order to assist in ensuring that air is uniformly removed in the manner explained below. A tube 4 communicates with groove 2 and leads to any convenient source of vacuum (not shown). Plate l is mounted on a hollow metal base 5 having an inner chamber 6 through which cooling water is adapted to be circulated. Printing area 3 may be painted black or it may be covered with a black piece of non-reflective paper or the like.

The photosensitive coated material 7 is placed upon such printing area 3 of plate 1 and the photonegative or photopositive transparency 8 is superimposed thereon. It is, of course, very important that the reproducing copy be in intimate contact with such coated photoresist material, and I accordingly place a clear piece of iiexible plastic sheet material 9 over the above assembly and extending laterally beyond groove 2. This flexible transparent plastic sheet may, for example, be of cellulose acetate, cellulose nitrate, cellulose propionate, cellulose butyrate, polyvinyl acetate, vinylidine chloride, melamine formaldehyde, methyl methacrylate, polyamides (nylon), and other well-known polymers and co-polymers. Such plastic sheet may be clamped to the outer border of plate 1 but, if thin and llexible enough, it may be retained in place and provided with an adequate seal simply through the action of the vacuum now produced in groove 2. Such vacuum, of course, draws down the plastic sheet firmly upon the superimposed photonegative and photosensitive coated material to press the same firmly and snugly together. After an exposure which may ordinarily be from about 2 to about l0 minutes depending on the light source, the thickness of the photosensitive coating, and the copy being reproduced, the vacuum may be relieved and the exposed photosensitive coated material removed. A considerable quantity of heat is normally produced and absorbed during this process and cooling Water will accordingly be circulated through chamber 6.

As shown in Fig. l of the drawing, the photosensitive coated material may comprise a permeable supporting base l0 of sheet material such as Yoshino long fiber paper coated on one side with the preferred light sensitive polymeric resin ll, or as shown in Fig. 2 such permeable sheet material may be coated on both sides with the resin iilm or layer 11. When the coated material of Fig. l is exposed to light passing through negative 8 having a light impermeable area 12, the coating 11 will include exposed and unexposed areas corresponding to the light transmitting and light impermeable areas of the negative. Thus, as shown in Figs. 4 and 5, the unexposed region 13 remains soluble and may be washed out by appropriate solvent development as shown in Fig. 5 to expose they underlying permeable material 10 in a sharply deined area i4 forming the stencil design. Similarly, as shown in Fig. 6, when both sides of the thin permeable layer l0 have been coated with the resin, the stencil design will be formed by solvent development of the underexposed regions 1S and 16 on directly opposite sides of permeable sheet 10. When both sides of sheet l0 are thus coated with the resin resist layers, it is especially important that sheet 10 be thin and of good light transmitting quality so that the resin on the underside of the sheet will be exposed suiiiciently to render the same insoluble. The resin on the underside of the sheet will, moreover, in such cases likewise preferably be in the form of a relatively thin film.

I have been successful in applying the resin to a permeable sheet in the form of a film as thin as such sheet itself and up to a thickness of 0.01 inch. Ordinarily, the resin film should have a thickness of from about .0015 to .O08 inch, and preferably from about .002 to .005 inch. The permeable supporting sheet will preferably be from 1/z mil to l mil in thickness for the production of fine line stencils and from l. to 3 mils in thickness for production of broad line stencils.

While Minsk et al. Patent 2,610,120 recommends a variety of solvents such as aromatic alcohols, ethers, ether alcohols, furfural, benzaldehyde, morpholine and aceto-phenone, for example, and either immersion of the coated plates therein or treatment by a technique resembling that followed in vapor degreasing, I employ resin coatings which may be of considerably greater thickness than those contemplated by Minsk et al., and accordingly I prefer to employ a hot developer at a temperature of from about 50 to 95 C. when employing a developer such as dichlor-ethylene and trichlor-ethylene. It is also desirable to maintain some slight motion of the stencil while immersed in the hot developer, or to circulate the latter, since otherwise incomplete washing out of the unexposed areas may be experienced.

I have found, however, that a different type of developer is more suitable for my purpose and may be employed without heating. Examples of such developers are Cellosolve acetate solvents such as ethylene glycol mono-methyl ether acetate, ethylene glycol mono-ethyl ether acetate, and ethylene glycol mono-butyl ether `acetates.

A wide variety of pervious supporting media may be employed in the manufacture of my new stencil, the life required and the type of copy to be reproduced largely dictating the selection of the particular medium to be employed. As above indicated, Yoshino long fiber pervious paper may be utilized and, if desired, such paper may be wet strengthened in the manner described in my co-pending application Serial No. 293,418 filed June 13, 1952. I prefer, however, to strengthen and reinforce the permeable material without blocking the pores or interstices therein by preliminarily coating such material (eg. Yoshino paper) with a resin solution of the type described herein as forming the photosensitive coating, but having only a relatively low solids content (less than 7% by weight, and preferably about 41/2%), and drying such coating. This dilute solution upon drying merely coats and bonds the fibers without substantially blocking or closing the pores or interstices and may then be exposed to light to render the same hard and insoluble. For example, as shown in Figure 9 the light-hardened material 18 coats and bonds the fibers 19. This pretreated material is now coated with the photo-sensitive resin as above described, the desired portions are exposed, and upon development the unexposed portions are washed out as before leaving the stencil design but with the stencil areas reinforced and wear-resistant. Not only is the pre-treated material compatible with the resist and firmly bonded thereto, but also the plasticizer in the developer (as described below) serves to plasticize the exposed reinforced areas for greater useful life. I have found that stencils so prepared may have their useful lives increased by as much as or 2() times. It is, moreover, now possible to produce electrolytic stencils having large open stencil areas Without the usual resist ligatures. The treated reinforced stencil areas are resistant to the electrolytes ordinarily employed.

If desired, the stencil areas only may be treated to reinforce the same after the stencil has otherwise been prepared but I ordinarily prefer to strengthen the entire permeable sheet prior to preparation of the stencil.

Instead of employing a dilute solution of the resin for such pre-treatment, a more concentrated solution may be employed together with an absorbent medium to adsorb the excess as described in the aforesaid application Serial No. 293,418, or suction may be applied. As the material is expensive, however, I prefer simply to use a dilute solution and to allow a somewhat longer drying time.

Excellent stencils have been produced using silk screen as the supporting medium, the life of the stencil being limited only to the wearability of the resin film resist. Another supporting medium is a very fine woven fabric of glass fiber. Nylon (polyamide resin), rayon (cellulose derivatives), Orlon (acrylic resins), Daeron (polyester resins), linen, cotton, wool, and metal cloth may all be employed. They should, of course, be selected to provide the proper uniform distribution of voids or interstices for passage of the marking material therethrough.

Inasmuch as I prefer to employ a resin resist film of substantially greater thickness than that contemplated by Minsk et al. in the production of their lithographie plates, I have encountered a certain amount of difficulty due to undesirable hardness or brittleness of such film. I have accordingly added plasticizers to the resin in amount up to byweight of the total weight of the solids present in the solution of the photosensitive resin or lacquer without any apparent deleterious effect upon the photosensitivity of the latter. Inasmuch as such lacquer is very expensive, the addition of the plasticizer not only renders the same more suitable for my purpose, but also serves considerably to reduce the cost thereof. Phthalates as a class and more particularly dimethyl phthalate, dibutyl phthalate, diamyl phthalate, dimethoxyethyl phthalate, and dibutoxyethyl phthalate have proven satisfactory. Organic phosphates as a class and more particularly tricresyl phosphate and triphenyl phosphate have likewise proven satisfactory. Orthonitrobiphenyl may also be used. In general, plasticizers for such resins are familiar to those skilled in the art and any suitable plasticizer may be employed.

It was expected that a considerable portion of the added plasticizer might be washed out of the resin film when the latter is subjected to the action of the developer. While some such effect has been apparent, the resin resist layer of the finished stencil has been sufhciently strong and flexible without local weak spots or unrelated voids.

I prefer, however, to incorporate the plasticizer in the developer (either the hot or cold type referred to above) as this method is very convenient and inexpensive and has been found to be unexpectedly effective. Nor does it interfere with the action of the developer.

It is often desired to incorporate some color into the finished product, and I have found that certain dies which are soluble in the organic solvents used with either the resin or the developer may be incorporated in suficient amount to impart quite dense color with no deleterious effect on the finished product. Malachite green, nigrosine black, wool fast blue, plasto blue, spirit blue, and other dies have been mixed into the photosensitive lacquer to impart the desired color to the film. While a certain proportion of the die may wash out during the developing operation, sufficient remains to achieve my purpose. The dies may in fact be dissolved in the developer which will thereupon impart color to the retained plastic film during the developing operation.

My new method of producing stencils is suitable for use with any copy which lends itself to photographing and from which a photonegative or photopositive transparency may be prepared. Where the number of copies desired is suicient to justify, entire pages of print, for example, may be reproduced in this manner and copies run off on a mimeograph machine. Half tones may be reproduced with excellent detail and stencils produced in accordance with my invention may readily be applied to the silk screen process. My new stencils are especially useful for employment with electrolytes for electrolytic etching and marking, particularly of metals. They have proved extremely wear-resistant, are not hydrophilic, and produce very sharp and denite outlines.

Reference may also be had to Allen Patent 2,566,302 which discloses copolymers suitable for employment in accordance with my invention. Styrene and l-cinnamyl styrene are copolymerized to form a resin Which I place upon my permeable supporting sheet. After exposure to light, the resist may be developed with a suitable solvent such as chlorobenzene, xylene, or decahydronaphthalene.

In general, I prefer to employ light sensitive polymeric cinnamic acid esters such as cinnamic acid esters of polyvinyl alcohol and cellulose, with their light sensitivity enhanced or fortified by inclusion of nitro compounds, anthrone compounds, quinone compounds, diaminodiphenyl carbinol, diaminodiphenyl methane, and diaminodiphenyl ketone compounds as taught in the previously mentioned Minsk et al. patents. These sensitized resins are light sensitive in the ultra-violet range. G. A. Schrter (Kunstoffe 4l, 291-4 (1951)) also describes a photosensitive resin which I may employ. Rubber hydrohalides and nitrocellulose are sensitized with iso-cyclic and heterocyclic compounds containing at least three ring systems, including compounds containing the ring systems of anthracine, acridine, and phenozine.

Other modes of applying the principle of the invention may be employed, change being made as regards the details described, provided the features stated in any of the following claims or the equivalent of such be employed.

I therefore particularly point out and distinctly claim as my invention:

1. The method o-f producing a wear-resistant stencil which comprises applying a very thin coating of a cinnamic acid ester resin sensitized to the action of light to a thin flexible sheet of porous material, such coating leaving the pores in such sheet open, exposing such coated sheet to the action of Ilight to render such coating insoluble, then coating such pre-coated sheet with a film of a cinnamic acid ester resin sensitized to the action of light and effective to close such pores in such sheet, drying such film to leave a residual coating having a thickness of from .0015 to .008 inch, superimposing an article having opaque and transparent areas, exposing such coated sheet to the action of light transmitted through such article to render the exposed portions insoluble in developer, and washing such exposed film in solvent developer to dissolve out the unexposed portions and disclose the underlying reinforced permeable sheet to produce the stencil design.

2. The method in accordance with claim l, including plasticizing of the exposed resin film simultaneously with such development operation.

3. The method of producing a wear-resistant stencil 7 which comprises coating a thin sheet ofV porous brous material with a lrn of cinnamic acid ester resin sensitized to the action of light, such ilrn being effective to coat thev fibers but insuicient toV block the pores in the sheet, exposing such coated sheet to the action of light to render the exposed portions insoluble, uniformly coating such pre-coated sheet with a lm of a cinnarnic acid ester resin sensitizedy to the action of light and suticient to block all pores in such sheet, superimposing au articleV having opaque and transparent areas, exposing such coated sheet to the action of light transmitted through such article to render the exposed portions insoluble in developer, and Washing such exposed film in solvent developer to dissolve out. the unexposed portions and disclose the underlying reinforced permeable sheet to producethe stencil design.

4. The method as set forth in claim 3, wherein the exposed portions of the resin lm are plasticized during the Washing operation by meansV of a plasticizer incorporated in the solvent developer.

5. A stencil comprising a sheet of porous material permeable to an electrolytic fluid, light-exposed decomposition products of a light-sensitized cinnarnic acid ester resin coating the porous material without closing pores therein to strengthen and reinforce said material, and av further coating of the light-sensitive cinnamic acid ester resin overlying and adhered to said sheet to close the pores thereof, said last mentioned resin being reactive to light to form hardened non-design areas of the stencil.

6. The stencil of claim wherein the further coating contains a nitro aryl compound as a light-sensitizer for the resin, said compound having a nucleus containing from 6 to 10 carbon atoms, from 1 to 3 nitro groups being attached to such nucleus, the mono-nitro compounds being free of amino, hydroxyl and formyl groups in a position ortho to the nitro group, such nitro aryl compounds being free of an amino and a hydroxyl group in positions ortho to each other, and free of carboxyl and sulpho groups.

7. A stencil for electrolytic marking comprising a flexible porous iibrous sheet permeable to an electrolytic uid, light-exposed decomposition products of a lightsensitized cinnamic acid ester resin coating the fibers of said sheet Without closing the pores thereof to strengthen and reinforce said sheet, and a exible plasticized Waterimpermeable coating of the light-sensitized cinnamic acid ester resin overlying and adhered to said sheet to close the pores` thereof, `said last mentioned resin being re# active, to light toI form hardened non-design areas of the stencil and thereby adapt the non-exposed areas forremoval to reveal the underlying coated fibers of said sheet.,

8. 'Ilhe stencil of clairn 7 wherein said resin includes approximately 20 percent plasticizer by weight.

9.. A stencil for electrolytic marking comprising a exible porous fibrous sheet from 0.5 mil to 3 mils iu thickness, light-exposed decomposition products of a light-sensitized cinnamic acid ester resin coating the bers of said sheet Without closing the porcs thereof to strengthen and reinforce said sheet, and a flexible plasticized Water-impermeable coating of a light-sensitized cinnamic acid ester resin overlying and adhered to said sheet effective to block all of the pores of the sheet and to form hardened stencil resist areas Where later subjected to the action of light, those areas not thus subjected being soluble in developer and thereby adapted for removal and subsequent passage of an electrolytic uid through such areas and the underlying juxtaposed areas of the coated fibers of the sheetso to effect an electrolytic marking.

10. The stencil of claim 9 wherein said resist coating has a thickness at least equal to the thickness of the permeable sheet and wherein said resin is an ester selected from the group consisting of the cinnamic acid ester resin of polyvinyl alcohol and the cinnamic acid ester resin of cellulose.

References Cited in the le of this patent UNITED STATES PATENTS 1,371,157 Gestetner Mar. 8, 1921 1,830,980r Carr Nov. 10, 1931 2,064,764 Playford et al. Dec. 15, 1936 2,131,225 Kirch Sept. 27, 1938 2,184,288 Danglemajer Dec. 26, 1939 2,335,021 Nestleberger Nov. 23, 1943 2,370,874 Playford Mar. 6, 1945 2,405,508 Lindsay Aug. 6, 1946 2,500,877 Sharples Mar. 14, 1950 2,557,352 Kanitz June 19, 1951 2,610,120 Minsk et al. Sept. 9, 1952 2,693,426 Hoover et al. Nov. 2, 1954 2,732,301 Robertson et al. Jan. 24, 1956 FOREIGN PATENTS 633,293 Great Britain Dec. 12, 1949 

1. THE METHOD OF PRODUCING A WEAR-RESISTANT STENCIL WHICH COMPRISES APPLYING A VERY THIN COATING OF A CINNAMIC ACID ESTER RESIN SENSITIZED TO THE ACTION OF LIGHT TO A THIN FLEXIBLE SHEET OF POROUS MATERIAL, SUCH COATING LEAVING THE PORES IN SUCH SHEET OPEN, EXPOSING SUCH COATED SHEET TO THE DACTION OF LIGHT TO RENDER SUCH COATING INSOLUBLE, THEN COATING SUCH PRE-COATED SHEET WITH A FILM OF A CINNAMIC ACID ESTER RESIN SENSITIZED TO THE ACTION OF LIGHT AND EFFECTIVE TO CLOSE SUCH PORES IN SUCH SHEET, DRYING SUCH FILM TO LEAVE A RESIDUAL COATING HAVING A THICKNESS OF FROM .0015 TO .008 INCH, SUPERIMPOSING AN ARTICLE HAVING OPAQUE AND TRANSPARENT AREAS, EXPOSING SUCH COATED SHEET TO THE ACTION OF LIGHT TRANSMITTED THROUGH SUCH ARTICLE TO RENDER THE EXPOSED PORTIONS INSOLUBLE IN DEVELOPER, AND WASHING SUCH EXPOSED FILM IN SOLVENT DEVELOPER TO DISSOLVE OUT THE UNEXPOSED PORTIONS AND DISCLOSE THE UNDERLYING REINFORCED PERMEABLE SHEET TO PRODUCE THE STENCIL DESIGN.
 5. A STENCIL COMPRISING A SHEET OF POROUS MATERIAL PERMEABLE TO AN ELECTROLYTIC FLUID, LIGHT-EXPOSED DECOMPOSITION PRODUCTS OF A LIGHT-SENSITIZED CINNAMIC ACID ESTER RESIN COATING THE POROUS MATERIAL WITHOUT CLOSING PORES THEREIN TO STRENGTHEN AND REINFORCE SAID MATERIAL, AND A FURTHER COATING OF THE LIGHT-SENSITIVE CINNAMIC ACID ESTER RESIN OVERLYING AND ADHERED TO SAID SHEET TO CLOSE THE PORES THEREOF, SAID LAST MENTIONED RESIN BEING REACTIVE TO LIGHT TO FORM HARDENED NON-DESIGN AREAS OF THE STENCIL. 